Expansible rotary drill bit



Jam@ 2, E96@ A. w. KAMMERER 2,949735 EXPANSIBLE ROTARY DRILL BIT Filed April l5, 1957 2 Sheets-Sheet 2 IN VEN TOR. ec//fe W'Hw/Wfeie United States Patent EXPANSELE ROTARY DRILL BIT Archer W. Kammerer, Fullerton, Calif., assigner, by

direct and mesne assignments, to Rotary (Dil Tool Company, Buena Park, Calif., a corporation of California Filed Apr. 15, 1957, Ser. No. '652,852 9 Claims. (Cl. Z55-76) The present invention relates to rotary drill bits, and more particularly to rotary drill bits of the expansible type adapted to be lowered through well casing to drill or enlarge a well bore below the casing to a greater diameter than the inside diameter of the casing itself.

Rotary drill bits of the expansible type ordinarily includeV a plurality ofV cutters disposed initially in retracted position, which are expanded outwardly to enlarge a previously drilled hole. The maximum size of the cutters that can be used is limited by the necessity of disposing them in a retracted position to pass through the well casing or into the previously drilled hole, or both. The size of the cutters places restrictions on the extent that they can enlarge the previously drilled hole, and thereby limits `the extent to which they can be expanded outwardly.

Accordingly, it is an object of the present invention to provide a rotary expansible drill bit having cutters that can occupy a retracted position and which can be exp anded outwardly to a greater extent than was heretofore possible, to enlarge a previously drilled hole to a substantially greater diameter than heretofore.

Another object of the invention is to provide a rotary expansible drill bit having a plurality of cutters capable of being nested adjacent one another when in retracted position, in which one of the cutters has a greater length than one or more of the other cutters to permit greater outward expansion of all cutters for the purpose of enlarging the well bore to a greater extent, the cutter of greater length operating upon the full annular formation area between the wall of the original hole and the wall of the enlarged hole.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of a form in which it may be embodied. This form is shown in the drawings accompanying and forming part of the present specification. It will now be described in detail, for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description isnot to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

Figure l is a longitudinal section, with parts shown in elevation, through an embodiment of the invention with the cutters in retracted position;

Figure 2 is a View similar to Fig. l illustrating the cutters in their fully expanded position, taken along the line 2 2 on Fig. 3;

Figure 3 is a cross-section taken along the line 3-3 on Fig. 1;

Figure 4 is a view corresponding to Fig. 3 illustrating, somewhat diagrammatically, the cutters after they have been expanded outwardly to their maximum extent;

Figure 5 is a view similar to Fig. 3 illustrating thecutter arrangement on a known design of drill bit;

Figure is a view corresponding to Fig. 4 illustrating the maximum extent of outward expansion ofthe cutter arrangement disclosed in Fig. 5.

'2,941,785'.E Patented June 2l, 1960 of a string of drill pipe B extending to the top of a well.`

bore, by means of which the drill bit is lowered through a string of well casing (not shown) to a region below thev casing shoe (not shown) where the hole enlarging operation is to commence. The general type of expansible drill bit shown in the drawings is both illustrated and described in Patent No. 2,545,036, to which attention certain structural details which scribed herein in detail.

The upper por-tion of the rotary drill bit consists of a tubular mandrel it) having an upper pin 1ly threadedly connected to the lower end of the string of drill` pipe B. This mandrel includes an upper kelly or drill stern member l2 slidably splined to the main body 13 of the bit, as. by having a lower non-circular portion 14 of the kelly adapted to be telescopically received in a socket i5 formed in the main bit body.

The mandrel l0 has a limited range of longitudinal movement within the body 13, its downward movement being determined by engagement of the lower end 16 of the kelly with an" inwardly directed body shoulder l7,.its upward movement being limited by engagement of an external shoulder or fits within a counterbore 19 in the body of the tool above its socket portion 15, with a cylinder head 20 secured to are not disclosed nor dedirected ange 22; adapted to engage of the head relative to the body. Upward movement of the head 20 with respect to the body is prevented by one or more split snap retainer rings 24 received within an internal groove 25 in the body Iand extending across the upper end` of thev cylinder head.

The upper end of the body 13 is closed by an annular upper guide me1nber26, including a depending portion Z7 received within the upper end of the body and adapted to rest uponV or be disposed closely adjacent the retainer, rings 24. This upper guide member hasl anV upwardly' tapering guide surface 28 in its ilange portion Z9 which. rests on the upper end of the body 13, the guide 'being' by a split wire snap' ringv Si), which may be round in cross-section, received within removably securedto the body an internal groove 3l in the body and also within an opposed external groove 32 in the guide itself. The ring groove 31, but,` when disposed therein, only extends partially'into the4 groove being of' sufficient lateral depth as to permit the wire ring to be disposed completely 26 is inserted into and re Stlmay completely lill the internal body guide groove 32, such therewithin when the guide moved from the upper portion of the bit body 13. When the upper guide 26 is inserted in the body 13, the ring:v

3u is forced completely within the groove 32 until the ring 3d comes opposite the body groove 31, whereupon it'can expand inherently outwardly the groove'31 and partly within the groove'32, thereby releasably assembling the guide member 26 to the body.

The tool body 13 has a mounted on it, including cutter supporting members 36,A 36a pivotally mounted in secured to the body. Each cutter supporting member 36,

36a depends fromahinge-pin 38 and terminatesvin a'. bearing supporting pin 60 inclined inwardly and down-A wardly. A side roller cutter 61 or 61a is rotatably' mounted on each bearing supporting pin, being mounted. and ball bearing. elementsr 62, 63.-l supporting pin 69.k The ball bear- 63 lockthe cutters against endwisemovef.` ment on the lbearing supporting pin 60, as wellr as trans# on antiffriction roller rollable .onthe bearing ing elements is invited for.

companion..

piston portion 18 of the kelly, whichr` and be received partly within plurality of expansible parts.

body slot 37 on hinge pins 3Sk mitting axial and radial thrusts between each cutter and its associated supporting pin. The roller bearing elements 62 transmit primarily radial thrusts between these parts. The manner of mounting the ball and roller bearing elements 62, 63 between the cutters` and bearing sup-V porting pins and of retaining them in place is specifically described in the above-mentioned Patent No. 2,545,036.

The cutter supporting members 36, 36a and cutters 61, 61a mounted thereon tend to occupy a retracted position substantially entirely with the confines of the main body 13 of the bit. These cutter supporting members and cutters are expandible outwardly to enlarge the sides of the well bore and to operate `upon a formation shoulder C that the cutters produce in the latter. To accomplish the expansion, each cutter supporting member 36, 36a has an inclined expander surface 64 on its inner portion` below the hinge pin 38 which tapers in a downward and inward direction. Each expander surface terminates in a lock surface 65 formed on the cutter supporting member. The outward expansion is accomplished by produc- 4ing relative longitudinal movement between the mandrel and the bit body 13, which will produce corresponding relative longitudinal movement between the cutter supporting members 36, 36a and a tubular member 66 of the mandrel. This tubular member includes a lower portion 67 slidable within a guide bushing 68 secured in a guide support 69 attached to the body and extending across the slotted region of the latter below the lock surface 65.

Located initially above the guide 69 and below the hinge pins 38 and in cutter supporting member recesses 70 is a mandrel lock and expander 71 having its outer surface 72 adapted to engage the expander surfaces 64 and the lock surfaces 65. The lock and expander 71 may be formed integrally with the tubular member 66, the upper end of the latter being piloted within` a socket 73 in the lower portion of the kellyv 12. An enlarged boss 74 on the tubular member engages a downwardly facing shoulder 75 on the kelly, the tubular member being held against the shoulder by a suitable split retainer ring 76 snapped into an internal groove 77 encompassing the kelly socket 73 and engaging a downwardly directed shoulder 7-8 formed on the tubular member boss. Leakage between the boss 74 and the wall of the kelly socket 73 is prevented by a suitable side seal in the form of a rubber O ring 79 disposed within a groove 80 in the kelly 12 and engaging the -boss 74.

The kelly 12 has a central fluid passage 81 therethrough communicating with vthe string of drill pipe B. Fluid pumped through this passage can pass into an aligned central passage 82 in the tubular member 66 and through a central nozzle 83 in its lower portion, whereby drilling mud or similar fluid can be pumped down through the tool for the purpose' of removing the cuttings from the well bore and ushing them up around the drill pipe to the top of the hole.

Assuming that the body 13 of the tool is elevated relatively along the tubular mandrel 10, the inclined expander surfaces 64 of the cutter supporting members will be shifted upwardly along the lock and expander portion 71 of the tubular member 66. During such upward shifting, the cutter supporting members 36, 36a and the cutters 61, 61a carried thereby will be pivoted about the hinge pins 38 Iand urged in an outward direction. Movement of the body 13 with respect to the tubular mandrel 10 can continue until the cutters 61, 61a have been shifted outwardly to their fullest extent, as determined by engagement of stop shoulders 88 on the cutter supporting members 36, 36a with companion shoulders 89 formed in the body on opposite sides of each body slot 37. When such engagement occurs, the lower end 16 of the kelly portion of the tubular mandrel 10 will engage the body shoulder 17, and the lock and expander 71 on the tubular member 66 will be disposed behind and in engagement 4 with the lock surfaces 65 on the cutter supporting member 66.

It is to be noted that the lock surfaces 65 on the cutter supporting member 36, 36a and the companion surfaces 72 on the lock and expander portion 71`of the tubular member `66 are substantially parallel to the axis of the drill bit, to prevent the reactive forces of the formation on the cutters 61, 61a from moving the latter inwardly. As a practical matter, it is preferred that the coengaging lock surfaces 65, 72 be inclined slightly in a downward4 direction toward the axis of the tool to insure releaseof the lock and expander portion 71 from the cutter supporting member 36, 36a when the latter and the cutters 61, 61a are to be shifted back to their retracted position.

The relative longitudinal movement between the tubular mandrel 10 and the body 13 of the tool for effecting outward expansion of the cutters 61, 61a is accomplished hydraulically. The counterbore .19 receiving the piston 18 of the drill stem member 12 is formed in the upper portion of the body 13 to provide the cylinder 21 having a cylinder wall 90 extending from a lower shoulder 91, dclining the bottom of the counterbore, to the location of the upper guide member 26. As was previously des' cribed, this upper guide member 26 closes the upper end of the body 13, and can also prevent foreign substances from moving down into the body through the use of a suitable wiper ring 92, which may be in the form of a rubber or rubber-like O ring disposed in an internal groove 93 in the upper guide and slidably and sealingly engaging the periphery of the mandrel 10. Y

The cylinder head 20, which is retained in the upper portion of the body cylinder 21, has an inner seal ring 94, in the form of a rubber or rubber-like O ring, received within an internal groove 9S in the cylinder head and slidably and sealingly engaging the periphery of the mandrel 10. This head 20 also has an external seal ring structure in the form of a rubber or rubber-like O ring 96 disposed in an external groove 97 in the head and sealingly engaging the wall 90 of the counterbore cylinder 21. The head 20 itself has a depending skirt 98 engaged by the upper end of the piston portion 18 of the mandrel for the purpose of limiting the extent of relative upward movement of the mandrel 10 with respect to the body 13 of the tool. This skirt 98 is disposed at the outer portion of the cylinder head 20 to provide an annular space 99 between the periphery of the mandrel or kelly 12 above the piston portion 1-8 and the skirt itself into which fluid under pressure from the central passage 81 of the mandrel can enter, such iluid iiowing through intercommunicating lateral ports 100 in the mandrel immediately above the piston portion 18.

Fluid from the cylinder space 99 is prevented from l passing downwardly around the periphery of lthe piston 18 by a suitable side seal ring 101, such as -a rubber or rubber-like 0 ring, disposed in a piston groove 102 and sealinglyk engaging the cylinder wall 90.

Fluid under pressure in the string of drill pipe B and within the tubular mandrel 10 is fed into the cylinder space 99 through the side ports 100, such fluid under pressure being developed by the back pressure built up through the necessity of the fluid to pass through the relatively restricted passage 82 through the tubular member 66 and the nozzle 83 at its lower portion. This back pressure imposed on the fluid in the cylinder space 99 acts in an upward direction on the cylinder head 20, urging the body 13 of the tool upwardly with respect to the tubular mandrel 10 and correspondingly elevating the cutter supporting members 36, 36m and cutters 61, 61a with respect to the lock and expander portion 71 of the tubular member 66, until the cutters 61, 61a are expanded to their fullest extent. Thus, with the fluid pressure elevating the body relative to the mandrel, the tool can be rotated, the cutters 61, 61a operating upon the formation and gradually being expanded outwardly as the body continues to be elevated along the mandrel until antigas the cutters have been expanded outwardly to their fullest extent, as determined by engagement of the cutter supporting arm shoulders 88 with the companion body shoulders 89. When this occurs, the mandrel and lock portion 71 is disposed behind companion lock surfaces 65 of the cutter supporting member 36, 36a, to retain the cutters 61, 61a in their outwardly expanded position, the downward drilling weight being transmitted from the lower end 16 of the kelly 12 to the body shoulder 17, and from the stop shoulders 89 on the latter on opposite sides of the slots 37 to the cutter supporting members 36, 36d, being transmitted from' the latter through the cutters 61, 61a to the formation shoulder C. The cutters 61, 61a will remain locked in their outwardly expanded position so long as drilling weight is being imposed upon the drill pipe B and the drill bit A, the cutters 61, 61a operating upon the formation shoulder C to progressively enlarge the bore in a downward direction. During the drilling operation, a guide D of any suitable form, which is mounted on the lower portion of the body 13, centers the drill bit in the original hole E. When expanded, the cutters 61, 61a will produce the enlarged hole F.

With the cutters 61, 61a in their outwardly expanded position, as disclosed in Fig. 2, down weight is imposed thereon and the drill bit rotated through the drill pipe, the cutters operating upon the formation shoulder C and enlarging the hole in a downward direction. After the desired length of hole has been enlarged, or the cutters have become Worn, the tool may be retrieved from the well bore by discontinuing the pumping of uid therethrough and elevating the drill pipe B and the mandrel attached thereto. Such action will elevate the lock portion 71 of the tubular member 66 above the lock surfaces 65 on the cutter supporting members 36, 36a, allowing the latter and the cutters 61, 61a carried thereby to move back to their retracted position, such as disclosed in Fig. l. The tool may now be elevated in the Well bore and moved back through the well casing to the top of the hole.

In the type of tool illustrated in the drawings, the bearing supporting pins 60 are disposed the same distance below the hinge pins 38, and all of the cutter supporting members 36, 36a and cutters 61, 61a areexpanded outwardly to the same extent, to drill the enlarged hole F. Heretofore, the cutters 61, 61a have all been made alike, having the same cutter length and the same diameter. With the same length of cutter supporting member 36, 36a and the same size cutter, the cutters would each have a certain maximum length, as dictated by the need for the cutters to be disposed in their fully retracted position substantially completely within the contines of the body 13, and by the fact that the cutters could only be located inwardly of the body to the point at which they did not interfere with one another. Such arrangement of cutters 61x is illustrated in Fig. 5, the outer portions of the cutters being disclosed in relation to the diameter ofthe previously drilled hole E which is to be enlarged.

With the cutter arrangement illustrated in Fig. 5, they can be expanded outwardly, as a practical matter, to increase the radius of the hole by an amount which corresponds to the length L of each cutter. That is to say, the length of the formation shoulder that is produced in the, well bore could be no greater than the length L of the cutter teeth, the cutter teeth extending from the inner wall of the drilled hole E to the inner wall of the enlarged hole F1. This condition is illustrated diagrammatically in Fig. 6. If the cutters 61x were expanded outwardly beyond the extent indicated, then the inner ends of the cutter teeth would be disposed outwardly ofV the inner wall of the hole E, and would not operate across the full face of the formation shoulder C, which would impede progress of the bit through failure to drill the hole, or which would result in the failure of the bit to make any progress at all. y

By virtue of the present invention, the cutters 61, 61a and the cutter supporting members 36, 36a can initially occupy a retracted position substantially completenl within the confines of the body 13 of the drill bit and can be expanded outwardly to a greater extent, in order to increase the size ofthe initial hole E to a much greater diameter than heretofore, assurance being had that the drill bit cutters will operate upon the full face of the shoulder C produced between the inner wall of the original hole E and the inner wall of the enlarged hole F, such as disclosed in Figs. 2 and 4.

In accomplishing the purposes of the present invenf tion, one ofthe cutters 61a is made longer than the other cutters 61. That is to say, the other cutters 61 are shorter in length L1 than the corresponding cutters 61x represented in Fig. 5, whereas the one cutter 61a is made longer in length L2 than the corresponding cutter represented in Fig. 5, this latter cutter 61a extending inwardly to a further extent than the corresponding cutter represented in Fig. 5. The outer portions of all of the cutters could be substantially the same, as illustrated in Fig. 2, such outer portions lying within the contines of the body 13 when in retracted position. The cutters 61, 61a arranged and proportioned as disclosed in Figs. l to 4, inclusive, can be expanded outwardly to a greater extent than Vthe cutter arrangement and proportions illustrated in Figs. 5 and 6, to enlarge the size of the bore hole E to a greater extent. As shown in Figs. 2 and 4, the c utter supporting members 36, 36a and the cutters v61, 61a have been expanded outwardly to a greater extent than shown in Fig. 6 to drill a hole F having a radius that is greater than the hole size F1 by the amount indicatedby the letter G in Fig. 6 In that ligure, the circle F represents the size of the enlarged hole drilled lby the cutter arrangement illustrated in Figs. l to 4 inclusive, whereas the letter F1 indicates the size of the enlarged hole that can be produced by the cutter arrangement and proportions shown in Fig. 5. The enlarged hole F will be produced with the cutter 61a operating upon the entire radial extent of the shoulder C, extending from the Wall of the original hole E, to the wall of the enlarged hole F. Such increase in expansion of the cutters to drill the increased hole size F is made possible by the fact that the length of the cutter 61o is greater than heretofore, so as to be capable of operating upon a shoulder C that is substantially greater than was heretofore possible. The greater size hole will be produced despite the fact that the length of the cutters 61 has been decreased. As shown in Figs. 2 and 4, the cutters 61 do not operate upon the inner `alltlntrlar portion H of the formation shoulder C. Despite this fact, the inner annular portion H of the shoulder C is still being operated upon by the inner portion of the teeth of the cutters 61a, as is clearly evident from Figs. 2 and 4. The cutters 61 cooperate with the` cutters 61a in performing by far the greater proportionv of the drilling action to enlarge the well bore from the size of the hole E to the size of the hole F. The amount of material that must be removed by the inner portion of the cutter 61a alone, represented by the annulus H in Fig. 2, is relatively small, and ksuch removal occurs without ditlicult-y.

it is, accordingly, apparent that a rotary drill bit has been provided in which the cutters can be expanded outwardly to ay greater extent to correspondingly enlarge the size of a preexisting well bore E to a greater asto the size of the well bore F, with assurance that all portions of the formation shoulder C lying between the inner wall ofthe original hole E and the inner wall of the enlarged hole F will be acted upon by at least one cutter ofthe apparatus. A substantial increase in the size of the enlarged hole is thereby made possible, the increase in the size of the enlarged hole being represented diagrammatically and by way of example by the letter G in Fig. 6.

Thev inventor claims:

l. In a hole enlarging rotary drill bit for operation extent, suchy outer portions of both of upon the formations in well bores to enlarge the well bores: a body; first cutter means mounted on said body for lateral movement vwith respect to said body; second cutter means mounted on said body for lateral movement with respect to said body; both of said cutter means being adapted to occupy a fully retracted position on said body closely adjacent one another and substantially entirely within the outer circumference of said body with said first cutter means extending inwardly of said body to a substantially greater extent than said second cutter means; and means engaging both of said cutter means and movable with respect to said body for expanding both of said cutter means outwardly of said body to the extent at which the inner cutting portion of said first 'cutter means extends substantially closer to the ax-is of the body than the inner cutting portion of said second cutter means, all of said inner 'cutting portions adjacent to the formation being disposed externally vof the outer circumerence'of said body when both of said cutter means are'in expanded position.

2. In a hole enlarging rotary drill bit for operation upon the formations in well bores to enlarge the well bores'. a body; first cutter means mounted on said body for lateral movement with respect to said-body; second cutter means mounted on said body for lateral movement with respect to said body; both of said cutter means being adapted to occupy a fully retracted position on said body closely adjacent one another and substantially entirely within the outer circumference of said body with the said cutter means being substantially equidistant from the axis of the body and with said rst cutter means extending inwardly of said body to a substantially greater extent than said second cutter means; and means engagnig both of said cutter means and movable with respect to said body for expanding both of said cutter means outwardly of said body to the same extent, whereby their outer portions are substantially Eequidistant from the body axis and the inner cutting por- Vtion of said iirst cutter means extends substantially closer to the axis of the body than the inner-cutting portion of 'said second cutter means, all of said innerV cutting portions adjacent to the formation being disposed externally of the outer circumference of said body when both of said cutter means are in expanded position.

3. In a hole enlarging rotary drill bit for operation upon the formations in well bores to enlarge the Well bores: a body; first cutter means mounted on said body for lateral movement with respect to said body; second cutter means mounted on said body for lateral movement with respect to said body; both of said cutter means'being adapted to occupy a fully retracted position on said body closely adjacent one another and substantially entirely within the outer circumference of said body with the outer portions of both of said cutter means being substantially equidistant from the axis of the body and with said first cutter means having a greater cutter length than said second cutter means and extending inwardlyfrorn its iouter portion to a substantially greater extent than said second cutter means; and means engaging both of said,

fcutter means and movable with respect to said body for expanding both of said cutter means outwardly of said body to the same extent, whereby their outer portions are :substantially equidistant from the body axis and the inner fcutting portion of said rst cutter means extends substantially closer to the axis of the body than the inner cutting portion of said second cutter means, all of said inner cutting portions adjacent to the formation being disposed externally of the outer circumference of said body when both of said cutter means are in expanded position.

4. In a hole enlarging rotary drill bit for operationV upon the formations -in well bores to enlarge the well bores: a body; a first supporting member mounted on said body for lateral movement with respect to said body; aiirst roller cutter rotatably mounted on said first sup.

porting member; la second supporting member mounted on said body for lateral movement with respect to said body; a second roller cutter rotatably mounted on said second supporting member; said supporting members and cutters being adapted to occupy a fully retracted position on said body with said first roller cutter closely adjacent said second roller cutter and extending inwardly of said body to a substantially greater extent than said second roller cutter, said retracted cutters being substantially entirely within the outer circumference of said body; and means engaging said supporting members and movable with respect to said body for expanding said supporting members and cutters outwardly of said body to the extent at which the inner cutting portion of said first cutter extends substantially closer to the axis of the body than the inner cutting portion of said second cutter, all of said inner cutting portions adjacent to the formation being disposed externally of the outer circumference of said body when both of said cutters are in expanded position.

5. In a hole enlarging rotary drill bit for operation upon the formations in Well bores to enlarge the well bores: a body; a first supporting 'member mounted on said body for lateral movement with respect to said body; a first roller cutter rotatably mounted on said first supporting member; a second supporting member mounted on said body for lateral movement with respect to said body; a second4 roller cutter rotatably mounted on said second supporting member; said supporting members and cutters being adapted to occupy a fully retracted position on said body with said cutters closely adjacent each other and substantially entirely within the outer circumference of said body, with the outer portions ofrboth of said cutters substantially equidistant from the axis of the body and w-ith said first cutter extending inwardly of said body to a substantially greater extent than said second cutter; and means engaging saidsupporting members and movable with respect to said body for expanding said supporting members and cutters outwardly of said body to the same extent, whereby the outer portions of said cutters are substantially equidistant from the body axis and the inner cutting portion of said first cutter extends substantially closer to the axis of the body than the inner cutting portion of said second cutter, all of said inner cutting portions adjacent to the formation being `disposed externally ofthe outer circumference of said body when both of said cutters are in expanded position.

6. In a hole enlarging rotary drill bit for operation upon the formations in well bores to enlarge the well bores: a body; a Ifirst supporting member mounted on said body for lateral movement with respect to said brxy; a first roller cutter rotatably mounted on said rst supporting member; a second supporting member mounted on said body for Alateral movement with respect to said body; a second roller cutter rotatably mounted on said second supporting member; said support-ing members and cutters being adapted to occupy a fully retracted position on said body with said cutters closely adjacent each other and substantially entirely within the outer circumference of said body, with the outer portions of both of said roller cutters substantially equidistant from the axis of the body, and with said first roller cutter having a greater cutter length than said second roller cutter and extending inwardly from its outer port'on to a substantially greater extent than said second roller cutter; and means engaging said supporting members and movable with respect tov to the axis of the body than the inner cutting portion of said second roller cutter, all of said inner cutting portions adjacent to the formation being disposed externally of the outer circumference of said body when both of Ysaid slutters are in expanded position.

7. In a hole enlarging rotary drill bit for operation upon the formations in well bores to enlarge the well bores: a body; a first supporting member mounted on said body for lateral movement with respect to said body; a first roller cutter rotatably mounted on said rst supporting member; a second supporting memberv mounted on said body for lateral movement with respect to said body; a second roller cutter rotatably mounted on said second supporting member; said cutters being rotatable on their respective supporting members about axes mak` ing a substantial angle to the body axis; said supporting members and cutters being adapted to occupy a fully retracted position on said body with said cutters closely adjacent each other and substantially entirely within the outer circumference of said body, with the outer portions of both of said roller cutters substantially equidistant from the axis of the body and with said first roller cutter having a greater cutter length than said second roller cutter and extending inwardly from its outer portion to a substantially greater extent than said second roller cutter; and means engaging said supporting members and movable with respect to said body for expanding said supporting members and cutters outwardly of said body to the same extent, whereby said cutters are operable upon a transverse formation shoulder in the well bore with their outer portions substantially equidistant from the body axis and the inner cutting portion of said first roller cutter extending substantially closer to the axis of the body than the inner cutting portion of said second roller cutter, all of said inner cutting portions adjacent to said shoulder being disposed externally of the outer circumference of said body when all of said cutters are in expanded position.

8. in a hole enlarging rotary drill bit for operation upon the formations in well bores to enlarge the Well bores: a body; three supporting members mounted on said body for lateral movement with respect to said body; a first roller cutter rotatably mounted on one of said supporting members; a roller cutter rotatably mounted on each of said other supporting members, said supporting members and cutters being adaptedto occupy a fully retracted position on said body with said iirst cutter closely adjacent said other cutters and the outer portions of all of said roller cutters substantially equidistant from the axis of the body, said irst roller cutter having a greater cutter length than both of said other cutters so as to extend inwardly of said body, when in retracted position thereon, to a substantially greater extent than said other roller cutters, said retracted cutters being substantially entirely within the outer circumference of said body; and means for expanding all of said supporting members and cutters outwardly of said body to the same extent, whereby the outer portions of all of said cutters are substantially equidistant from the body axis and the inner cutting portion of said first roller cutter extends substantially closer to the axis of the body than the inner cutting portions of said other roller cutters, all of said inner cutting portions adjacent to said formation being disposed externally of the outer circumference of said body when all of said cutters are in expanded position.

9. In a hole enlarging rotary drill bit for operation upon the formations in well bores to enlarge the Well bores: a body; a iirst supporting member mounted on said body for lateral movement with respect to said body; a first cutter mounted on said lirst supporting member; a second supporting member mounted on said body for lateral movement with respect to said body; a second cutter mounted on said second supporting member; said supporting members and cutters being adapted to occupy a fully retracted position on said body with the outer portions from the axis of the body and the inner portions of said cutters closely adjacent one another; both of said cutters having cutter teeth extending laterally of the axis of the body, said first cutter having a greater cutter length than said second cutter so as to extend inwardly from its outer portion, when in retracted position on said body, to a substantially greater extent than said second cutter, said retracted cutters being substantially entirely within the outer circumference of said body; and means engaging said supporting members and movable with respect to said body for expanding said supporting members and cutters outwardly of said body to the same extent, whereby the outer portions of said cutters are substantially equidistant from the body axis and the inner cutting portion of said first cutter extends closer to the axis of the body than the inner cutting portion of said second cutter, all of said inner cutting portions adjacent to the formation being disposed externally of the outer circumference of said body when both of said cutters are in expanded position.

References Cited in the le of this patent UNITED STATES PATENTS 1,835,108 Arthur et al. Dec. 8, 1931 2,367,637 Zublin Jan. 16, 1945 2,545,036 Kammerer Mar. 13, 1951 2,687,785 Morlan et al. Aug. 31, 1954 2,758,819 Kammerer Aug. 14, 1956 FOREIGN PATENTS 3,194 Austria Jan. 25, 1901 of both of said cutters substantially equidistant 

